Paper gripper mechanism



Aug. 6, 1963 R. H. EICHORN PAPER GRIPPER MECHANISM Filed Dec. 23, 1960 2 Sheets-Sheet 1 INVENTUR. ROGER H. EICHORN ATTORN EY Aug. 6, 1963 R. H. ElcHoRN PAPER GRIPPER MECHANISM 2 Sheets-Sheet 2 Filed Dec. 25, 1960 INVENTOR ROGER H. Elon-ORN vm mmm vm,

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fw mmm Gm ATTO R N EY Y United States Patent O 3,169,1439 PAPER GRIPPER MECHANllSM Roger H. Eichorn, Webster, NY., assigner to Xerox Corporation, a corporation of New York Filed Dec, 23, 1960, Ser. No. 77,956 8 Ciairns. (Qi. 27h-7% This invention relates in general to xerographic reproducing apparatus and, in particular, to a sheet gripper mechanism for a sheet conveyor to permit seriatim feeding of sheets of transfer material to a xerographic drum.

Specifically, the invention relates to an improved sheet gripper mechanism for a sheet conveyor that is particularly adapted for use in a xerographic reproducing machine, and which is also suitable for use with comparable types of devices.

In prior sheet feeding devices of the type having conveyor chains adapted for the transport of a sheet gripper device for feeding sheets of paper, or the like, to a cylinder, such as an offset cylinder in a printing press, it has been customary to provide a recess in the cylinder adapted to receive the sheet gripper so that a sheet carried thereby may be brought into contact with the cylinder.

In a xerographic reproducing apparatus of the type in which the xerographic plate is formed in the shape of a drum, it is necessary in the transfer process, when using sheet material, to bring the sheet material into contact with the peripheral surface of the xerographic plate without parts of the conveyor mechanism transporting this sheet coming into contact with the photoconductive insulating surface of the xerographic plate. Since it is des'irable, for reasons which need not be described in detail herein, to have a continuous layer of photoconductive insulating material on the xerographic drum, it is apparent that a recess cannot be formed in the xerographic drum to receive the sheet gripper of a conveyor mechanism.

It is, therefore, the principal object of this invention to improve a sheet gripping device for use in the sheet feeding apparatus of a xerographic machine, the sheet gripping device being adapted for seriatim feeding of sheets to a rotating drum without the sheet gripper device contacting lthe Xerographic drum.

Another object of this invention is to improve sheet gripping devices for use in a sheet conveyor whereby various sized sheets of paper, or like material, are conveyed into proper registered contact with a xerographic drum, or like device.

For a better understanding of the invention as Well as other objects and further features thereof, reference is had to the following detailed description of the invention to be read in connection with the accompanying drawings, wherein:

FIG. 1 is a schematic illustration of a Xerographic apparatus lincorporating a sheet feed mechanism having paper gripper mechanisms constructed in `accordance with the invention;

FIG. 2 is an enlarged top view of a preferred embodiment of a paper mechanism constructed in accordance with the invention;

FIG. 3 is a view of the 3 3 of FIG. 2;

FIG. 4 is an enlarged sectional view taken along line 4 4 of FIG. 2;

FIG. 5 is an enlarged sectional View taken along line 5 5 of FIG. 2; and,

IFIG. 6 is an enlarged sectional View taken along line 6 6 of FIG. 2.

Referring now to the drawings, there is shown in FIG. l a xerographic reproducing apparatus used for producing xerographic reproductions from a moving original.

The xerographic reproducing apparatus is adapted for paper gripper taken along line installation within a suitable light-tight housing or cabinet of a size so that the entire unit may be mounted on an oiiice desk or table.

General As shown, the xerographic apparatus comprises a xerographic plate including a photoconductive layer or lightreceiving surface on ya conductive backing and formed in the shape of a drum, generally designated by numeral 20, which is journaled in a frame to rotate in the direction indicated by the arrow to cause the drum surface sequentially to pass a plurality of xerographic processing stations.

For the purpose of the present disclosure, the several xerographic processing stations in the path of movement of the drum surface may be described functionally as follows:

A charging station, at which charge is deposited on the xerographic drum;

An exposure station, at which a light or radiation pattern of copy to be reproduced is projected onto the drum surface to dissipate the drum charge in the exposed areas thereof and thereby form a latent electrostatic image of the copy to be reproduced;

A developing station, at which a xerographic developing material including toner particles having an electrostatic charge opposite to that of the electrostatic latent limage are cascaded over the drum surface, whereby the toner particles adhere to the electrostatic latent image to form a xerographic powder image in the configuration of the copy to be reproduced;

A transfer station, at which the xerographic powder image is electrostatically transferred from the drum surface to a transfer material or support surface; and

A drum cleaning and discharge station, at which the drum surface is rst charged and then brushed to remove residual toner particles remaining thereon after image transfer, and at which the drum surface is exposed to a relatively bright light source to effect substantially complete discharge of any residual electrostatic charge remaining thereon.

The charging station is by reference character the apparatus.

a uniform electrostatic photoconductive layer of the preferably located as indicated A in the schematic illustration of In general, the charging apparatus or corona charging device 21 includes a corona discharge array of one or more discharge electrodes that extend transversely across lthe drum surface and are energized from a high potential source Iand are substantially enclosed within a shielding member.

Next subsequent thereto in the path of motion of the Xerographic drum' is an exposure station B. This exposure station may be one of a number of types of mechanisms or members such `as desirably an optical scanning or projection system or the like designed to project a line copy image onto the surface of the photoconductive xerographic drum from a suitable original.

The opt-ical scanning or projection assembly consists of a copyboard in the shape of a drum, hereinafter referred to as copy drum 22, which is adapted to support copy to ybe reproduced and yarranged to rotate in light-projection relation to the moving light-receiving surface of the xerographic plate. Uniform lighting is provided by suitable lamps attached to -a slotted light -reliector 23 mounted adjacent to the copy drum. l

A light shield 24 adapted to protect the xerographic plate from extraneous light is positioned adjacent to the surface of the xerographic plate. A slot aperture 26 in the light shield extends transversely to the path of movement of the light-receiving surface of the xerographic drum 20 to permit reflected rays from the copy drum to be directed against a limited transverse area of the light-receiving surface as it passes therebeneath.

To enable the optical system to be enclosed within a relatively small cabinet, a -folded optical system including an object mirror 26, -a lens 27, and an image mirror 28 is used in the preferred embodiment of the apparatus.

Copy fed through paper guides 31 to the copy drum is removably secured thereon by a suitable gripper mechanism for movement therewith in timed relation to the movement of the xerographic drum whereby a Vowing image of the copy is projected onto the xerographic drum. The copy is held against the surface of the copy drum' by means of guides 32 and 33, the latter also preventing the trailing edge of the copy from contacting the web cleaner 54. After the copy is scanned it can be released from the copy drum to be transported out of the machine by copy feed out roller 34 coactng with the peripheral surface of the copy drum to forward the copy through copy guide 30.

Adjacent to the exposure station is a developing station C in which there is positioned a developer apparatus 3S including a developer housing having a lower or sump portion for accumulating developer material 36. Mounted within the developer housing is a motor driven buckettype conveyor used to carry the developer material previously supplied to the developer housing to the upper portion of the developer housing from where the developer material is cascaded over a hopper chute onto the drum.

As the developer material cascades over the drum, toner paritcles of the developer material adhere electrostatically to the previously formed electrostatic latent image areas on the drum to form a visible xerographic powder image; the remaining developer material falling ofi the peripheral sur-face of the drum into the bottom of the developer housing. Toner particles consumed during the developing operation to form the xerogra-phic powder images are replenished by a toner dispenser 37, of the type disclosed in copending application Serial No. 77,955, filed concurrently herewith on December 23, 1960, in the name of Roger H. Eichorn and William G. Lewis, mounted within the developer housing.

Positioned next adjacent to the developing station is the image transfer station D which includes suitable sheet feeding mechanism Aadapted to feed sheets of paper successively to the xerogr-aphic drum' in coordination with the presentation of the developed image on the drum at the transfer station. The sheet vfeeding mechanism includes a sheet source such as tray 41 for a plurality of sheets of a suitable support material, that is, sheets of paper or the like, a separator roller 42 adapted to feed the top sheet of the stack of support material to a sheet conveyor mechanism 43 having paper grippers 44 thereon which carry the sheet support material into contact with the rotating xerographic drum in coordination with the appearance of a developer image at the transfer station.

The transfer of the xerographic powder image from the drum surface to the support material is effected by means of a corona transfer device 4S that is located or at immediately after the point of contact between the support material and the rotating xerographic drum. The corona transfer device 45 is substantially similar to the corona discharge device that is employed at the charging station in that it also includes an array of one or more corona discharge electrodes that are energized from ta suitable high potential source and extend transversely across the drum surface and are substantially enclosed with a shielding member. In operation, the electrostatic field created by the corona transfer device is effective to tack the transyfer material electrostatically to the drum surface and simultaneously with the tacking action, the electrostatic field is elfective to attract the toner particles comprising the xerographic powder image from the drum surface and cause them to adhere electrostatically to the surface of the support material.

As the paper gripper mechanism continues to move forward in its closed circuit, it will strip the support material `from the xerographic drum yand carry it to a fixing device, such as, for example, heat fuser 46, whereat the developed and transferred xerographic powder image on the support material is permanently fixed thereto.

After fusing, the finished copy is preferably discharged from the apparatus at a suitable point for collection externally of the apparatus. To accomplish this there is provided a pair of ydelivery rolls 47 and y48 by means of which the copy is delivered to a copy holder after it is released by the Igripper mechanism. Suitable cam means are pnovided at the receiving and delivery stations of the conveyor mechanism to actuate the paper gripper at these stations to receive or discharge a sheet of support material.

The next and nal station in the device is a drum cleaning station E whereat any powder remaining on the xero- 'graphic drum after the transfer step is removed and whereat the xerographic idrum is flooded with light to cause dissipation of any residual electrical charge remaining on the xerographic drum.

To aid in the removal of any residual powder remaining on the xerographic drum there is provided a corona precleanin-g device 51 that is substantially similar to the corona discharge device that is employed at charging station A. Removal of residual powder from the xerographic drum is effected by means of a web cleaner device 54 adapted to continuously feed a clean fibrous web material into wiping contact with the Xerographic drum. As shown, the web material 55 is taken from a supply roll 56 and transported around a cleaning roll V57, preferably made of rubber, around a guide plate 58 to be wound on a take-up or rewind roll 61.

Any residual electrical charge remaining on the xerographic drum is dissipated by light from a iiuorescent lamp 62 mounted in a suitable bracket above the xerographic drurn, a suitable starter being provided for energizing the 4fluorescent lamp.

Suitable drive means drive the xerographic drum, the copy drum, the sheet conveyor mechanism at predetermined speeds relative to each other, and to effect operation of the paper separator roll, and fthe web cleaner mechanism, the latter being driven at a speed whereby relative movement between the xerographic drum and the 'web material is effected. Suitable drive means are also provided for effecting operation of the conveyor mechamsm and toner dispenser of the developing apparatus assembly.

It is believed that the lforegoing description is sufficient for the purposes of this application to show the general operation of a xerographic reproducing apparatus. For further details concerning the specific construction of the xerographic apparatus shown, reference is made to copending application, Serial No. 77,954, filed concurrently herewith on December 23, 1960, in the name of Roger H. Eichorn and William G. Lewis.

Referring now to the subject matter of the invention, the paper -grippcrs carried by the chains of the sheet conveyor are used to transport a sheet of support material into contact with the peripheral surface of the xerographic drum. Since the peripheral surface of the xerographic drum is continuous, that is, no slots are formed therein to. receive the sheet grippers, the sheet grippers must be capable of advancing a sheet of support material into contact with the peripheral surface fof the xerographic drum without the gripper itself coming into contact therewith. Since both of the paper grippers used in the machine are of like construction, for simplicity, only one will Ibe described herein.

As sholwn in detail in FIGS. 2 to 6, inclusive, a preferred embodiment of a paper gripper 44, constructed in accordance with the invention, consists of a gripper bar 391 of a length to extend substantially between the two roller chains 361 to be connected thereto .by means of clips 388 forming part of the chains when connected thereto, as is well known in the art. The clips 388 are formed to support the gripper bar so that the top surface of the gripper bar is positioned slightly below the pitch line of the chains, whereby the gripper bar as it passes beneath the xerographic drum will not contact the peripheral surface of the xerographic drum.

A concave sheet gripper jaw 392, which may be a separate element fixed to the gripper 'bar Aor as shown c.formed integral therewith, extends across the rear of the gripper bar (in terms of the direction of travel of the `gripper bar). The concave sheet gripper jaw is positioned to have surface contact with the leading edge of a sheet of support material as it is advanced from the paper guide 39. The concave sheet gripper jaw cooperates with the tang portions yor jaws 39S of the grippers 394 to grip a sheet of support material inserted therebetween.

Each of the grippers is mounted, by means of pins 398 suitably secured to the leading edge of the gripper bar, for movement in two directions relative to the fixed ooncave sheet gripper jaw 392; that is, for movement from a frst position in which the tangs or jaws of the gripper are in spaced-apart relation to the concave sheet ygripper jaw to receive a sheet of support material therebetween, and for movement to a second position in which the tangs or jaws of the gripper are in engagement with the concave sheet gripper jaw or with a sheet of support material sandwiched therebetween. Springs 399 encircling the pins 398 are positioned with one end of the springs abutting the underside of the gripper bar and the other end of the springs abutting the cam follower portion 397 of the gripper to normally bias the tangs or jaws of the gripper into contact with the concave sheet gripper jaw o1' with a sheet of support material inserted therebetween. To prevent .cocking of the grippers, each gripper is provided with a `depending curved guide portion or tang 396 which is slidably received in a suitable slot 393 formed in the gripper bar 391, the tang also serving as a guide or stop for the leading edge 0f the support material..

A sheet of support material gripped between the concave sheet gripper jaw and the tangs or jaws of the grippers is arched upward into contact with the drum as it passes therebeneath because of the shape of the concave sheet gripper jaw which tends to slightly bend the leading edge of a sheet as shown in FIG. 18.

Referring now to FIG. 14, a sheet of suppont material, such as paper, forwarded into the paper yguide 39 by the action of separator roller 4,2 is slightly wrinkled as the separator roller `continues to advance the sheet after its forward motion has been arrested by the gate 355. Thus, as a paper gripper advances over lche guide, the gate 355 will be forced open as the paper gripper strikes it and at the same time the cam followers 397 of the grippers will strike the cam 65, fastened to cam supports 387 adjustably secured to iframe plates It@ and 11, to open the jaws of the paper gripper to receive the sheet from the paper guide 39. Because of the slight buckle in the sheet and because at this time the separating roller is still attempting to advance the sheet, the sheet :as it unbuckles will be forced between the jaws of the paper gripper so that as the cam followers of the grippers slide off the cams the jaws will close by the biasing action of lthe springs 399 to grip the sheet and forward it to the delivery station of the machine.

At the delivery station, the paper gripper passes between the delivery rollers 47 and 4S and as it does so, the grippers are again actuated by means of their cam followers riding over the cam 6d secured to the shoulder portions :of the left-hand and right-hand conveyor supports, thereby releasing the sheet from the paper gripper for discharge from the machine.

While the invention has been described with reference to the structures disclosed herein it is not confined to the details set forth and this application is intended to cover such modifications or changes as may come within the 6 purposes of the improvements or the scope of the following claims.

What is claimed is:

1. In a sheet feeding apparatus having conveyor chains adapted to transport a sheet gripping device fnom a sheet receiving station to a sheet delivery station, wherein the sheet gripping device includes a gripper bar secured to said conveyor chains transversely therebetween, a sheet gripper jaw portion on said gripper bar serving as a common lower gripper jaw, a plurality of grippers pivotably secured on said gripper bar, each of said grippers being pivotally mounted on said gripper bar, each of said grippers having jaw portions thereon adapted to coopcrate with said sheet gripper jaw portion to grip a sheet therebetween, and .cam follower portions on each of said grippers adapted t-o be actuated by cams located adjacent and between said conveyor chains at said sheet receiving station and said sheet delivery station, and springs operatively connected to said gripper bar and to each of said cam follower portions of sa`d grippers to normally bias said jaw portions` of said grippers into cooperative engagement fwith said sheet gripper jaw.

2. In a sheet feeding apparatus having conveyor chains adapted to transport a sheet gripping device from a sheet receiving station to a sheet delivery station, wherein the sheet gripping device includes la gripper bar secured to said conveyor chains transversely therebetween, said gripper bar, having a common lower concave sheet gripper jaw, a plurality of grippers pivotably secured to said gripper bar, each of said grippers having jaw portions thereon adapted to cooperate with said concave sheet gripper jaw to lgrip the leading edge of a sheet therebetween and to buckle a sheet so gripped to force a portion thereof to extend above said gripper bar, and cam follower portions on each of said grippers adapted to be actuated .by cams located adjacent Iand between said conveyor chains at said sheet receiving station and said sheet delivery station, and springs. operatively connected to said gripper bar and to each of said cam follower portions of said grippers to normally bias said jaw portions of said grippers into cooperative engagement with said concave sheet gripper jaw.

3. In a sheet feeding apparatus having conveyor chains adapted to transport a sheet gripper device from a sheet receiving station to a sheet delivery station, wherein the sheet gripping device includes a gripper bar secured to said conveyor chains transversely therebetween, a concave sheet gripper jaw portion on said gripper bar serving as 1a common lower gripper jaw, a plurality of pins secured to the leading edge of said gripper blar, a plurality of grippers pivotably secured to said pins on said gripper bar, eac-h of said grippers having jaw portions thereon adapted to sheet a pontion thereof to extend above said gripper bar, 'and cam follower petitions on each :of said grippers adapted to be actuated by cams located adjacent and between said conveyor chains at said sheet receiving station and said sheet delivery station, and springs operatively connected to said pins, one end Aof said springs being in contact with each of said cam follower positions of said grippers and its opposite end in contact with said gripper bar to normally bias said jaw portions of said grippers into cooperative engagement with said concave sheet gripper jaw.

4. In a sheet feeding apparatus having a pair of conveyor chains adapted to transport a sheet gripping device from a sheet receiving station to a sheet delivery station, wherein the sheet gripping device includes a gripper bar secured to said conveyor chains transversely therebetween, said gripper bar having a concave depressed portion at its trailing edge with respect to its direction of travel as carried by said conveyor chains, a plurality of grippers pivotably secured to said gripper bar, each of said grippers having jaw portions thereon adapted to cooperate with said concave depressed portion of said gripper bar to grip the lead-ing edge ofv a sheet therebetween and to buckle the sheet while engaged therebetween to force a portion of the sheet to extend above said gripper bar and said grippers, and cam follower portions thereon adapted to be actuated by cams located adjacent and between said conveyor chains at said sheet receiving station and said sheet delivery station, and springs operatively connected to said gripper bar and to said grippers to normally bias said jaw portions of said grippers into cooperative engagement with said concave depressed portion of said gripper jaw.

5. In a sheet feeding apparatus having a pair of conveyor chains adapted to transporta sheet gripping device from a sheet receiving station to a sheet delivery station, wherein the sheet gripping device includes a gripper bar secured to said conveyor chains transversely therebetween, said gripper bar having a cornrn'on concave sheet gripper jaw portion thereon at its trailing edge with respect to its direction of travel, and apertures therein positioned between said sheet gripper jaw portion and the leading edge of said gripper bar; a plurality of grippers pivotably secured to said gripper har. each of said grippers having jaw portions thereon adapted to cooperate with said concave sheet gripper jaw to grip the leading edge of a sheet therebetween `and to buckle a sheet so gripped to force a portion thereof to extend above said gripper bar, cam follower portions on each of said grippers adapted to -be `actuated by cams located adjacent and between said conveyor chains lat said sheet receiving station and said sheet delivery stati-on, and a depending tang on each of said grippers positioned to extend through one of said apentures adapted to guide the leading edge of a sheet; and springs operatively connected to said gripper bar and to said each of said cam follower portions of said geippers to normally bias said jaw portions of said grippers into cooperative engagement with said concave sheet gripper jaw portion of said gripper bar.

6. In la sheet feeding apparatus having a pair of conveyor chains adapted to transport a sheet gripper device from a sheet receiving station to a sheet delivery station, wherein the sheet gripping device includes a grippery bar secured to said conveyor chains transversely therebetween, a concave sheet gripper jaw portion on said gripper bar serving as a common lower gripper jaw, and apertures therein positioned between said gripper jaw portion and the leading edge of said gripper bar; a plurality of pins secured to the leading edge of said gripper bar, a plurality of grippers pivotably secured to said pins on said gripper bar, each of said grippers having jaw portions thereon adapted to cooperate with said concave sheet gripper jaw to grip the leading edge lof a sheet therebetween and to buckle a sheet so gripped to force a portion thereof to extend above said gripper bar, a depending t-ang positioned to extend through one of said apertures to guide fthe leading edge of a sheet, and cam follower pontions thereon adapted to be actuated by cams located adjacent and between said conveyor chains at said sheet receiving station and said sheet delivery station; and coil springs encircling said pins, one end `of said coil springs being in contact with each of said cam follower pontions of said grippers and its opposite end contact 8 with said gripper bar to normally bias said jaw portions of said grippers into cooperative engagement with said concave sheet gripper jaw portion.

7. ln a sheet feeding apparatus having a pair of conveyor chains adapted to transport a sheet gripping device from a sheet receiving station to a sheet delivery station, wherein the sheet gripper device includes a gripper bar secured to said conveyor chains transversely there.- between, said gripper bar having a common lower sheet gripper jaw portion thereon at its trailing edge with respect to its direction of travel, said gripper bar having apertures therein positioned between said sheet gripper jaw portion and the leading edge of said gripper bar; a plurality of grippers pivotably secured to said gripper, each of sm'd grippers having jaw pontions lthereon Iadapted to cooperate with said sheet gripper jaw to grip the leading edge of a sheet therebetween, each of said gr-ippers having cam follower portions thereon adapted to be actuated by cams located 'adjacent and between said conveyor chains at said sheet receiving station and said sheet delivery station, and each of said grippers having a de.- pending tang portion positioned to extend through one of said apertures to guide the leading edge of ia sheet, and springs operatively connected to said gripper bar and to said each of said cam follower portions of said grippers :to normally bias said jaw portions of said grippers into cooperative engagement with said sheet gripper jaw portion of said gripper bar.

8. In a sheet feeding apparatus having a pair of conveyor chains adapted to transport a sheet gripper device from a sheet receiving station to a sheet delivery station, wherein the sheet gripping device includes a gripper bar secured to said conveyor chains transversely therebetween, a sheet gripper jaw portion on said gripper bar serving as a common lower ygripper jaw, said gripper bar having apertures therein positioned between said gripper jaw portion and the leading edge of said gripper bar with respect to its direction of travel; 1a plurality of pins secured to the leading edge of said gripper bar, a plurality of grippers pivotably secured to said pins on said gripper bar, each of said grippers having jaw portions thereon adapted to cooperate with said sheet gripper jaw to grip the leading edge of a sheet therebetween, each of said grippers having a depending tang positioned to extend through one of said apertures to guide the leading edge of a sheet, each of said grippers having cam follower portions thereon adapted to be actuated by cams located adjacent and between said conveyor chains at said Sheet receiving station and said sheet delivery station, and coil springs encircling said pins, said coil springs being in contact at one end with each of said cam follower portions of said grippers and at the opposite end in contact with said gripper bar to normally bias said jaw portions of said grippers into cooperative 4engages-lent with said sheet gripper jaw portion.

References Cited in the le of this patent UNITED STATES PATENTS 1,697,142 White Nov. i6, 1926 2,374,668 Davidson May l, 1945 2,882,049 Koch 1 Apr. 14, 1959 2,950,914 Golding Aug, 30, i960 UNITED STATES PATENT OFFICE CERTIFICATE 0F CORRECTION Patent No. 3,100,109 August 1963 Roger H. Eichorn It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 3, line 28, for "paritcles" read particles line 53, for "developer" read developed same column 3, line 56, for "or at" read at or column 6, line l0, strike out "pivotab1y"; line 28, after "bar" strike out the comme; column 7, line 4, for "the sheet while engaged therebetween" read a sheet so gripped line 5, for "of the sheet" read thereof same column 7, line for "thereon" read on each of said grippers Signed and sealed this 4th day of August 196MLl (SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER Aitesting Officer Commissioner of Patents 

1. IN A SHEET FEEDING APPARATUS HAVING CONVEYOR CHAINS ADAPTED TO TRANSPORT A SHEET GRIPPING DEVICE FROM A SHEET RECEIVING STATION TO A SHEET DELIVERY STATION, WHEREIN THE SHEET GRIPPING DEVICE INCLUDES A GRIPPER BAR SECURED TO SAID CONVEYOR CHAINS TRANSVERSELY THEREBETWEEN, A SHEET GRIPPER JAW PORTION ON SAID GRIPPER BAR SERVING AS A COMMON LOWER GRIPPER JAW, A PLURALITY OF GRIPPERS PIVOTABLY SECURED ON SAID GRIPPER BAR, EACH OF SAID GRIPPERS BEING PIVOTALLY MOUNTED ON SAID GRIPPER BAR, EACH OF SAID GRIPPERS HAVING JAW PORTIONS THEREON ADAPTED TO COOPERATE WITH SAID SHEET GRIPPER JAW PORTION TO GRIP A SHEET THEREBETWEEN, AND CAM FOLLOWER PORTIONS ON EACH OF SAID GRIPPERS ADAPTED TO BE ACTUATED BY CAMS LOCATED ADJACENT AND BETWEEN SAID CONVEYOR CHAINS AT SAID SHEET RECEIV- 